Scatterometry has been used extensively for the characterization of critical dimensions (CD) and detailed side-wall profiles of periodic structures in microelectronics fabrication processes. Scatterometry can provide accurate and high-precision measurement for 2D and 3D structures used in integrated circuits. One source of error, e.g., from one optical system to another, is an angular error in the plane-of-incidence (POI) azimuth angle, which is the angle of POI of the probe beam (or reflected beam) and a reference direction that is in the plane of the sample.
Many scatterometry systems do not attempt to control the POI azimuth angle error. Advanced scatterometry, however, demands a high degree of alignment accuracy of the measurement target orientation relative to the plane-of-incidence (POI). When left uncontrolled, the angular error in the POI azimuth angle will generate a spectral signature that will varies from one system to another. Accurate hardware alignment, e.g., down to 0.2°, however, is extremely difficult to achieve.